Plating catalyst and method

ABSTRACT

A catalyst solution includes a precious metal nanoparticle and a polymer having a carboxyl group and a nitrogen atom. The catalyst solution is useful for a catalyzing an electroless process for plating metal on non-conductive surfaces.

This application claims the benefit of priority under 35 U.S.C. §119(e)to U.S. Provisional Application No. 61/582,265, filed Dec. 31, 2011, theentire contents of which application are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a catalyst solution including aprecious metal nanoparticle. More particularly, the present inventionrelates to a catalyst solution including a precious metal nanoparticlestabilized by specific compounds useful in electroless metal plating ofnon-conductive substrates used in the manufacture of electronic devicesand decorative coating.

BACKGROUND OF THE INVENTION

Electroless metal deposition or plating is useful for the deposition ofa metal or mixture of metals on a non-conductive or dielectric surfacein the absence of an electric source. Plating on non-conductive ordielectric substrates covers a wide range of applications, includingdecorative plating and electronic device fabrication. One of the mainapplications is the manufacture of printed circuit boards. Theelectroless deposition of a metal on a substrate usually requirespretreatment or sensitization of the substrate surface to make thesurface catalytic to the deposition process. Various methods have beendeveloped to catalyze the substrate.

U.S. Pat. No. 3,011,920 discloses a method to catalyze a substrate byimmersion of the substrate in the colloidal catalyst solution preparedby palladium ions with stannous ions to form a palladium-tin colloid.This method requires a step of acceleration after catalyzing thesubstrate surface whereby the catalyst core is exposed. U.S. Pat. No.3,904,792 discloses an improvement of colloidal palladium-tin catalyststo provide catalyst in less acidic environments. Hydrochloric acid ispartially replaced by a soluble salt of the acid. Such a palladium-tincatalyst systems present a number of limitations. The outer shell of thecatalyst colloid (SnCl₄)²⁻ is easily oxidized, thus the catalystparticles grow in size and lose their catalytic surface areadramatically.

U.S. Pat. No. 4,725,314 discloses a process for preparing a catalyticadsorbate in aqueous solution using an organic suspending agent toprotect the colloid with a maximum dimension not exceeding 500angstroms. Polyvinyl pyrrolidone may serve as an organic suspendingagent.

Because of the high cost of palladium, considerable effort has beenfocused on the development of non-noble metal catalyst systems. U.S.Pat. No. 3,993,799 discloses the use of a non-noble metal hydrous oxidecolloid for treating non-conductive substrates followed by reduction ofthe hydrous oxide coating on the substrate to achieve at least a degreeof activation for subsequent electroless plating. U.S. Pat. No.6,645,557 discloses a method to form a conductive metal layer bycontacting the non-conductive surface with an aqueous solutioncontaining a stannous salt to form a sensitized surface followed bycontacting the sensitized surface with an aqueous solution containing asilver salt having a pH in the range from about 5 to about 10 to form acatalyzed surface.

JP10229280A discloses a catalyst solution which is composed of silvernitrate or copper sulfate, as well as an anionic surfactant, such aspolyoxyethylene lauryl ether sodium sulfate and a reducing agent such assodium borohydride. JP11241170A discloses a non-palladium catalyst whichincludes at least one of iron, nickel, cobalt and silver salt, inconjunction with an anionic surfactant and a reducing agent.

JP200144242A discloses a manufacturing method for preparation of a highdispersing colloidal metal solution with high conductivity, whichcontains at least one amino group and one carboxyl group. U.S. Pat. No.7,166,152 discloses a sliver colloid based pretreatment solutioncomprising three components: (i) sliver colloidal particles; (ii) one ormore ions selected from metal ions having an electric potential whichcan reduce a sliver ion to silver metal in the solution; and (iii) oneor more ions selected from a hydroxycarboxylate ion, a condensedphosphate ion and an amine carboxylate ion. Normally, aqueous solutionsof colloidal tin-free silver are much more stable than those systemsinvolving stannous ions, which are easily oxidized to tin (IV) with airagitation. Colloidal silver catalyst systems would reduce cost and beless unstable than palladium systems. Such colloidal silver catalystsystems also show promising catalytic properties in electroless platingprocesses without sacrificing the interconnect reliability. Therefore, acolloidal catalyst system which has a balance of bath stability,adsorption capability and catalytic activity at the same time isdesired.

SUMMARY OF THE INVENTION

A solution includes a precious metal nanoparticle and a polymer, thepolymer has a carboxyl group and a nitrogen atom within the repeatingunit of the polymer.

A process for electroless plating a metal on non-conductive surfaceincludes dipping a substrate to be plated into a solution which includesa precious metal nanoparticle and a polymer, the polymer has a carboxylgroup and a nitrogen atom within the repeating unit of the polymer andconducting electroless plating of the substrate without an acceleratingstep.

Inventors of this invention have now found that a precious metalcolloidal catalyst system, which includes precious metal nanoparticlesstabilized by a specific type of polymer having carboxyl groups andnitrogen atoms and are tin-free show good stability and promisingcatalytic activity in electroless plating.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification the abbreviations given below havethe following meanings, unless the content clearly indicates otherwise:g=gram; mg=milligram; ml=milliliter; L=liter; m=meter; cm=centimeter;min.=minute; s=second; h=hour; ppm=parts per million; M=molar; g/L=gramsper liter; mmol=millimoles; Mw=molecular weight; rpm=revolutions perminute; and DI=deionized.

As used throughout this specification, the word “deposition” and“plating” are used interchangeably. The word “catalyzing” and“activating” are used interchangeably throughout this specification. Theword “solution comprising precious metal nanoparticles” and “catalystsolution” are used interchangeably throughout this specification.

The present invention provides a solution for electroless platingincluding a precious metal nanoparticle and a polymer having a carboxylgroup and nitrogen atom. The polymer used in this invention requiresboth a carboxyl group and a nitrogen atom. Preferably, the polymer hasboth a carboxylic group and a nitrogen atom within its repeating unit.As shown later, the solution which includes a polymer having both acarboxyl group and a nitrogen atom obtains better results with a stablecatalyst solution in comparison with a solution having polymers withnitrogen atoms but no carboxyl group, such as polyacrylamide andpolyvinyl pyrolidone. Though not wishing to be bound by theory, it isbelieved that carboxyl group is more important for the electrostericstabilization of nanoparticles, while nitrogen atom is useful for thenanoparticles adsorption.

A polymer used in this invention requires a polymer. As shown later,inventors of the present invention conducted comparative examples for asolution containing L-aspartate instead of the polymer. L-aspartate is alow molecular weight compound having a carboxyl group and nitrogen atom.The nanoparticles prepared with L-aspartate are not as stable as thoseprepared with the polymer, and it could only be stabilized in alkalinepH medium. In addition, the results of backlight tests for a solutioncontaining L-aspartate was poor compared to the results of a solutioncontaining a polymer having a carboxyl group and a nitrogen atom.

The molecular weight (Mw) of the polymer for the composition is 400 to1,000,000, more preferably, 1000 to 10,000.

The polymer useful for this invention is preferably polyamino acids andtheir copolymers. Examples of polyamino acids or their copolymersinclude polyaspartic acid, polyglutamic acid, polycyanophycin, copolymerof L-aspartic acid and L-alanine, copolymer of L-aspartic acid andglycine, copolymer of L-glutamic acid and glycine, copolymer ofphenylalanine and glycine.

Other preferable polymers include copolymers of monomers having amidestructures and monomers having carboxyl groups. Examples of a monomerhaving an amide structure are acrylamide, methacrylamide,vinylpyrrolidinone, N-(hydroxymethyl)methacrylamide) and2-acrylamido-2-methypropane sulfonic acid. Examples of a monomer havingcarboxyl group are acrylic acid, methacrylic acid, maleic acid andcitracomic acid.

The preferable amount of this polymer is 0.05 to 20 g/L, morepreferably, 0.5 to 5.0 g/L, based on the total amount of catalystsolution.

Precious metal nanoparticles of the present solution are provided by anyprecious metal having catalyst activity. Examples of precious metal aresilver, gold, platinum, palladium, rhodium, ruthenium, iridium andosmium. Preferable the precious metal is silver.

Mixtures of precious metals can be used, such as a mixture of silver andpalladium. The amount of precious metal nanoparticles is 10 to 20000ppm, preferably 100 to 10000 ppm, most preferably 200 to 5000 ppm basedon the weight of the solution.

The ratio of metal and a polymer having a carboxyl group and nitrogenatom in the present solution is determined by moles of metal andcarboxylic groups in the polymer, such as from 1:0.1 to 1:10,preferably, from 1:0.5 to 1:5.

Optionally, the present invention may include one or more of variousadditives common in electroless plating catalyst compositions, such assurfactants, buffers, complexing agents and pH adjuster. pH adjuster mayinclude bases such as, but not limited to, sodium hydroxide andpotassium hydroxide, and acids such as, but not limited to, sulfuricacid, oxalic acid, acetic acid, citric acid and other simple carboxylicacids. The amount of pH adjusters is based on the target pH value.

A solvent used in the present invention is preferably water, such as tapwater or DI water. Any other solvent such as alcohol or mixtures ofsolvents may be used for the present invention whenever the solvent canmix with water.

Typically, the present solution has a pH of 3 to 10. The preferable pHof the present solution depends on the type and amount of polymers andreducing agents in nanoparticle preparation procedure. Preferably, thetypical present solution has the pH of more than 4, more preferably, thepH is 6 to 9, and still more preferably, the pH is alkaline, that is ithas a pH of more than 7 to 9.

The present solution has stable solutions of nanoparticles useful as acatalyst for electroless plating for non-conductive surface of amaterial to be plated. Preferably, the present solution does not form avisually observable precipitate. More preferably, the present solutiondoes not form a visually observable precipitate after accelerated agingtests and accelerated shelf life tests. Extreme aging conditions havebeen tested, such as storage in 40° C. with air bubbling, hightemperature and low temperature storage.

The solution of the present invention can be prepared by combining aprecious metal ion, a polymer and a reducing agent in a solution.Preferably, the method for preparing a solution of this invention is (a)preparing a solution including precious metal ion and a polymer having acarboxyl group and a nitrogen atom, and (b) adding a reducing agent inthe solution, under stirring.

The precious metal ion used in the present invention is provided by anyprecious metal source whenever the precious metal is solvent soluble.Organic or inorganic acids can be used with precious metal sources tohelp dissolve the precious metals into solution. Precious metal elementsare selected from those which are described above, such as silver, gold,platinum, palladium, rhodium, ruthenium, iridium and osmium, and thepreferable precious metal element is silver as described above.

Preferable precious metal ion sources are organic or inorganic salts ofprecious metals. Examples of preferable precious metal ion sourcesinclude, metal nitrates, metal nitrites, metal halides, metal oxides,metal acetates, metal sulfates, metal sulfites, metal cyanides, metalgluconates, metal fluoroborates, metal alkylsulfonates, metalthiosulfates and metal thiocyanate. Examples of metal salts include,without limitation, silver nitrate, silver acetate, silver sulfate,silver methanesulfonate, silver p-toluenesulfonate, silver benzoate,silver phosphate, silver trifluoroacetate, palladium nitrate, palladiumchloride, palladium sulfate, palladium acetate, sodiumtetrachloropalladate, ammonium tetrachloropalladate, palladiumdichlorodiammine and palladium dichlorotetraammine.

The amount of the precious metal ions depend on the solubility of themetal salt and the desired concentration of precious metal nanoparticlesin the solution of the present invention. For example, silver salts maybe used in amounts of 0.01 to 100 g/L, preferably, 0.1 to 10 g/L, morepreferably, 0.1 to 5.0 g/L as metal, based on the total amount ofcatalyst solution.

The reducing agent used for reducing the precious metal ions is any ofthose reducing agents capable of reducing dissolved precious metal ionsto a reduced precious metal form without formation of by-products thatwould interfere with catalysis of the catalyst solution. Preferablereducing agents are dimethylamino borane, sodium borohydride, hydrazine,sodium hypophosphite, hydrazine hydrate, ascorbic acid, iso-ascorbicacid, hydroxylamine sulfate, formic acid and formaldehyde.

The amount of reducing agent is any amount sufficient to reduce thedesired precious metal ions. The preferable amount of reducing agent maybe decided by the ratio of the precious metal, such as 0.5 to 2 times bythe moles of precious metal ions. Typically, the amount is 0.01 to 10g/L, more preferably, 0.01 to 2 g/L, based on the total amount of metalconcentration in the catalyst solution and the choice of reducing agentused in the reaction.

The method for preparing a solution of the present invention is, (a)preparing a solution comprising precious metal ions and a polymer havinga carboxyl group and a nitrogen atom and (b) adding a reducing agent insaid solution under stirring the solution.

The first step of the method is preparing a solution including preciousmetal ions and a polymer having a carboxyl group and a nitrogen atom.The solution which includes the precious metal ions and the polymer canbe prepared by any method. For example, dissolve the polymer in asolvent such as water, then add a salt of precious metal or aqueoussolution of precious metal salt into the solution; or dissolve aprecious metal ion in a solvent, then add the polymer or a solution ofthe polymer into the solution.

The second step of the method is to add a reducing agent in the solutionunder stirring. The amount of reducing agent used in this step is anyamount sufficient to form the desired precious metal nanoparticles.

Reducing agent is added in the above solution under stirring. Understrong stirring conditions, the metal ions may be reduced to metal andquickly form nanocrystals which serve as seeds for further nanoparticlegrowth. If the stirring is inadequate, the particles size may benon-uniform and some of the particles may grow larger and mayprecipitate easily. In other words, strong stirring allows formation ofsmaller nanoparticles in a narrower particle size distribution. Thetypical mixing rates may be from 200 to 1000 rpm.

The temperature of the solution during the second step is 10 to 40° C.,typically around room temperature or 20° C.

Though not wishing to be bound by theory, the inventors believe that themechanism of forming stable precious metal nanoparticles in the presenceof the polymer of this invention is as follows: generally, thenanoparticles have a tendency to collide with each other due to Brownianmotion, convection, gravity and other forces, which may result inaggregation and destabilization of the colloid. Electrostaticstabilization and steric stabilization of colloids are the common twomechanisms for colloid stabilization. With the presence of polymer, theas prepared nanoparticles may be surrounded by the polymeric molecules,and the polymeric molecules create a repulsive force counterbalancingthe attractive Van der Waals force among particles.

A preferred method for preparing colloidal catalyst solutions ispreparing a solution which includes 1 to 5 g/L of silver ions and 1 to 5g/L of sodium polyaspartate, then adding 10 to 80 mmol/L ofdimethylamino borane under strong stirring or 200 to 800 rpm at 20 to40° C.

The solution containing a precious metal nanoparticle and a polymerhaving a carboxyl group and nitrogen atom can be used in the electrolessplating process for printed circuit boards. Through-holes are formed inthe printed circuit board by drilling or punching or any other methodknown in the art. After the formation of the through-holes, the boardsare rinsed with water and a conventional organic solution to clean anddegrease the board is applied followed by desmearing the through-holewalls. Typically desmearing of the through-holes begins with applicationof a solvent swell. Any conventional solvent swell may be used todesmear the through-holes. Solvent swells include, but are not limitedto, glycol ethers and their associated ether acetates. Conventionalamounts of glycol ethers and their associated ether acetates may beused. Such solvent swells are well known in the art. Commerciallyavailable solvent swells include, but are not limited to, CIRCUPOSITCONDITIONER™ 3302 solution, CIRCUPOSIT HOLE PREP™ 3303 and CIRCUPOSITHOLE PREP™ 4120 solutions all obtainable from Rohm and Haas ElectronicMaterials, Marlborough, Mass.

Optionally, the through-holes are rinsed with water. A promoter is thenapplied to the through-holes. Conventional promoters may be used. Suchpromoters include sulfuric acid, chromic acid, alkaline permanganate orplasma etching. Typically alkaline permanganate is used as the promoter.An example of a commercially available promoter is CIRCUPOSIT PROMOTER™4130 solution available from Rohm and Haas Electronic Materials.

Optionally, the through-holes are rinsed again with water. A neutralizeris then applied to the through-holes to neutralize any residues left bythe promoter. Conventional neutralizers may be used. Typically theneutralizer is an aqueous alkaline solution containing one or moreamines or a solution of 3 wt % peroxide and 3 wt % sulfuric acid.Optionally, the through-holes are rinsed with water and the printedcircuit boards are dried.

After desmearing an acid or alkaline conditioner may be applied to thethrough-holes. Conventional conditioners may be used. Such conditionersmay include one or more cationic surfactants, non-ionic surfactants,complexing agents and pH adjusters or buffers. Commercially availableacid conditioners include, but are not limited to, CIRCUPOSITCONDITIONER™ 3320 and CIRCUPOSIT CONDITIONER™ 3327 solutions availablefrom Rohm and Haas Electronic Materials. Suitable alkaline conditionersinclude, but are not limited to, aqueous alkaline surfactant solutionscontaining one or more quaternary amines and polyamines. Commerciallyavailable alkaline surfactants include, but are not limited to,CIRCUPOSIT CONDITIONER™ 231, 3325, 813 and 860 solutions available fromRohm and Haas Electronic Materials. Optionally, the through-holes arerinsed with water after conditioning.

Conditioning is followed by microetching the through-holes. Conventionalmicroetching compositions may be used. Microetching is designed toprovide a micro-roughened copper surface on exposed copper, e.g.innerlayers and surface etch, to enhance subsequent adhesion ofdeposited electroless and electroplate. Microetches include, but are notlimited to, 60 g/L to 120 g/L sodium persulfate or sodium or potassiumoxymonopersulfate and sulfuric acid 2% mixture, or generic sulfuricacid/hydrogen peroxide. An example of a commercially availablemicroetching composition includes CIRCUPOSIT MICROETCH™ 3330 solutionavailable from Rohm and Haas Electronic Materials. Optionally, thethrough-holes are rinsed with water.

A pre-dip is then applied to the microeteched through-holes. Any acidicsolution capable of removing copper oxides on copper surface withoutinterfering with the catalyst solution can be used. Examples of pre-dipsinclude oxalic acid, acetic acid, ascorbic acid, phenolic acid,phosphoric acid, boric acid, and salts thereof. Optionally, thethrough-holes are rinsed with cold water.

A catalyst, a solution including a precious metal nanoparticle, asdescribed above is then applied to the through-holes. The walls of thethrough-holes are then plated with copper with an alkaline electrolesscomposition. Any conventional electroless plating bath may be used. Acommercially available electroless copper plating bath includes, but arenot limited to, CIRCUPOSIT™ 880 Electroless Copper plating solutionavailable from Rohm and Haas Electronic Materials.

After the copper is deposited on the walls of the through-holes, thethrough-holes are optionally rinsed with water. Optionally, anti-tarnishcompositions may be applied to the metal deposited on the walls of thethrough-holes. Conventional anti-tarnish compositions may be used.Examples of anti-tarnish compositions include ANTI TARNISH™ 7130 andCUPRATEC™ 3 compositions obtainable from Rohm and Haas ElectronicMaterials. The through-holes may optionally be rinsed with hot water attemperatures exceeding 30° C. and then the boards may be dried.

The following examples are intended to further illustrate the inventionbut are not intended to limit its scope.

EXAMPLES Test Method

The properties of a catalyst were evaluated by observing electrolesscopper plating of a test coupon according to the process describedbelow. A conventional FR-4 laminate, SY-1141 (normal T_(g)) test couponfrom Shengyi was used. For surface coverage test a bare laminate wasused. For backlight testing a Cu clad laminate with an inner layer ofcopper was used.

-   (1) The test coupon was cut into 1×6 cm² pieces, and its edges were    sandblasted by SiC#240 particles, then cleaned in RO (Reverse    Osmosis) water for several times and blow dried.-   (2) Processing was done through the swelling, oxidizing,    neutralizing, conditioning and microetching steps shown in table 1.-   (3) The test coupon was dipped in the catalyst solution at 40° C.    for 3-10 minutes at specific pH described in each Example. The test    coupon was washed with deionized water.-   (4) Electroless copper plating was done at 40° C. for 15 minutes.

TABLE 1 Process flow for electroless Cu deposition tests TemperatureDuration Rinse time Process Components Volume [° C.] [min] [min] 1Sweller Hole Promoter 211 12.5% 80 7 3 CUPOSIT ™ Z 10.0% 2 OxidizerOxidizer 213A-1 10.0% 80 10 3 CUPOSIT ™ Z 15.0% 3 NeutralizerNeutralizer 216-5  5.0% 42 5 3 4 Conditioner Cleaner  3.0% 43 5 4Conditioner 231 5 MicroEtch Sodium Persulfate 75 g/L RT 2 3 H₂SO₄  2.0%6 Catalyst Ag: 300 ppm 30.0% 40 10 3 7 Electroless CIRCUPOSIT ™ Nil 4015 2 Copper 880 Electroless Copper

1. Plating Coverage Test

The plating coverage test for the coupon was assessed using the platingcoverage grading scale defined below.

Full coverage—more than 95% of the area on the surface of the testcoupon was plated.High—more than 75% and less than 95% of the area on the surface of testcoupon was plated.Medium—more than 50% and less than 75% of the area on the surface oftest coupon was plated.Low—more than 5% and less than 50% of the area on the surface of testcoupon was plated.No Coverage—less than 5% of the area on the surface of test coupon wasplated.

2. Backlight Test

The backlight test was conducted according to the process below.

1-mm-thick cross sections from each board were placed under aconventional optical microscope of 50× magnification in its transmissionmode. The quality of the copper deposit was determined by the amount oflight that was observed under the microscope and compared with theEuropean backlight Grading Scale (0-5). If no light was observed, thesection was completely black and was rated 5.0 on the backlight scale.This indicated complete copper coverage. If light passed through theentire section without any dark area, this indicated very little to nocopper metal deposition on the walls and the section was rated 0. Ifsections had some dark regions as well as light regions, they were ratedbetween 0 and 5 comparing with the standard.

3. ICD Test

Reliability of plating was measured by the following ICD test(Interconnect defects test)

A drilled MLB (multi-layer board) coupon was cut containing at least 30holes with hole diameters of 1 mm. The coupon edge was ground by SiCpaper with Grit#240.Ultrasonic cleaning was done in RO water for several times. The processwas run from desmear to PTH (plated through hole) and finally to copperelectroplating. Any Cu on each edge of the coupon was ground away. Thecoupon was backed at 125° C. for 6 h. The coupon was cooled down in drycabinet. An alternative solder dip was done at 288° C. for 10 seconds,cooled at room temperature for 110 seconds. The cycle was repeated 6times.Micro-section was performed on the coupon and it was investigated forICDs before etching. The number of defects were counted in theinterconnecting regions and calculated as the rate.The coupons were etched with an ammonia solution of 20 ml ammoniumsolution, 20 ml water and 10 drops hydrogen peroxide. The number ofdefects on the ICD was confirmed.

Example 1 Ag-PASP Catalyst System

Step 1: 1.0 g of polysuccinimide was mixed with 200 ml of deionizedwater with stirring and then 10 ml/L of 1.0 mol/L sodium hydroxidesolution were added into the mixed solution with stirring and withheating at 30-90° C. The Mw of the compound obtained was around 1100measured by GPC method.Step 2: 200 ml of the above solution was mixed into 800 ml of deionizedwater and 1.7 g of silver nitrate was added into the solution withstirring.Step 3: 10 ml of freshly prepared 2.0 mol/L dimethylaminoborane (DMAB)was quickly added into the above solution with strong stirring at 500rpm using magnetic stirrer. Stirring was done for over 2 h.

Accelerated aging test was conducted based on air bubbling of a testingsolution at a rate of 10 mL/min under a temperature bath maintaining at40° C. After one month, the catalyst solution was still in a good state.

Accelerated shelf life test at −20° C. and 60° C. for 48 hours was alsoconducted and there was no visually observable precipitate and nocatalytic activity loss.

Example 2 Ag-PASP Catalyst System

Step 1: 3.2 g of 40% sodium polyaspartate (PASP) solution(Mw=3,000-5,000) was mixed with 990 ml of deionized water with stirring.1.7 g of silver nitrate was added into the solution with stirring.Step 2: 10 ml of freshly prepared 2.0 mol/L dimethylaminoborane (DMAB)was quickly injected into the above solution with strong stirring at 500rpm using a magnetic stirrer. Stirring was done for over 2 h. Theresulting solution had pH of 9.0.

The accelerated aging test and accelerated shelf life test of Example 1were conducted and no precipitate or turbidity was observed.

Examples 3-13 Ag-PASP Catalyst Systems

Ag-PASP catalyst solution was prepared as in Example 2 except theconcentration of each ingredients and temperature were changed as shownin Table 2.

TABLE 2 Ag PASP DMAB Temperature Example (ppm) (g/L) (mmol/L) (degreeC.) pH 3 1080 0.85 20 27.2 7.8 4 1080 1.27 20 26.5 7.9 5 1080 1.69 2027.2 8.0 6 1080 2.12 20 26.8 8.0 7 1296 1.27 24 26.2 7.4 8 1512 1.27 2827.4 7.3 9 1728 1.27 32 27.7 7.2 10 1080 1.27 20 21.6 8.5 11 2160 2.5440 20.4 8.2 12 3240 3.81 60 20.9 8.0 13 4320 4.08 80 21.5 7.8

The performance tests were conducted on Example 2. The results of thecoverage test, backlight test and ICD test were shown in table 3. The pHwas adjusted using sulfuric acid or sodium hydroxide.

TABLE 3 Test pH 2.9 4.0 4.5 5.2 9.0 Coverage Full Full Full Full MiddleBacklight 4.5 4.5 4.5 2.9 — ICD (%) — <0.3% <0.3% — —

Examples 14-21 Ag-PGA Catalyst System

Ag-polyglutamic acid solution was prepared as in Example 2 except thatPASP was changed to polyglutamic acid (PGA) (Mw>500,000) and theconcentration of each ingredient was changed as shown in Table 4.

TABLE 4 Ag polyglutamic DMAB Temperature No. (ppm) acid (g/L) (mmol/L)(degree C.) pH 14 1080 0.2 20 24.3 5.7 15 1080 0.5 20 24.4 5.8 16 10801.0 20 24.5 5.9 17 1080 2.0 20 24.7 6.2 18 1080 0.5 20 25.3 5.6 19 10802.0 20 25.5 6.2 20 1080 3.2 20 25.7 6.2 21 1080 4.5 20 25.7 6.2

The performance tests were conducted on Example 19. The results of thecoverage test and backlight test are shown in Table 5.

TABLE 5 Test pH 3.0 4.0 5.0 Coverage Full Low No Backlight 4.7 — —

Examples 22-25 Ag-Copolymer of AA and AMPS Catalyst System

Ag-copolymer of Acrylic acid (AA) and 2-acrylamido-2-methypropanesulfonic acid (AMPS) solution was prepared as in Example 2 except PASPwas changed to a copolymer of Acrylic acid and2-acrylamido-2-methypropane sulfonic acid (Mw=10,000), and theconcentration of each ingredient was changed as shown in Table 6.

TABLE 6 Ag AA/AMPS DMAB Temperature No. (ppm) (g/L) (mmol/L) (degree C.)pH 22 540 1.0 10 18.1 4.0 23 1080 1.0 20 18.2 3.8 24 1620 1.0 30 18.13.6 25 2160 1.0 40 18.2 3.5

The performance tests were conducted on Example 24. The results ofcoverage test and backlight test are shown in Table 7.

TABLE 7 Test pH 3.5 5.0 7.0 Coverage Full High No Backlight 4.25 4.0 —

Comparative Example 1 Ag-ASP Catalyst System

Ag-L-aspartate solution was prepared as in Example 2 except PASP waschanged to L-aspartate (ASP), DMAB was changed to NaBH₄, and theconcentration of each ingredient was changed as shown in Table 8.

TABLE 8 Ag L-aspartate NaBH4 Temperature No. (ppm) (g/L) (mmol/L)(degree C.) pH 1 216 1.95 8 26.3 10.2

The performance tests were conducted on Comparative Example 1. Theresults of coverage test and backlight test are shown in Table 9.

TABLE 9 Test pH 9.9 Coverage (35 degree C.) Full Coverage (40 degree C.)Full Backlight 3.5

The nanoparticles prepared with L-aspartate were not as stable as thoseprepared with polyaspartate, and it could only be stabilized in alkalinepH medium, while the nanoparticles prepared with polyaspartate were ableto be stabilized in a broader pH range of 4-10.

Comparative Examples 2-5 Ag-PAM Catalyst System

Attempts were made to obtain Ag-polyacrylamide (PAM) solution as inExample 2 excepting PASP was changed to 0.2-2.0 g/L of PAM, and theconcentration of each ingredient was changed as shown in Table 10.

TABLE 10 Ag DMAB Temperature No. (ppm) PAM (g/L) (mmol/L) (degree C.) pH2 1080 0.2 10 24.5 5.37 3 1080 0.4 10 25.3 5.70 4 1080 1.0 10 25.8 5.765 1080 2.0 10 25.8 5.77However, with the addition of 0.2 or 0.4 g/L of PAM as stabilizer andafter 10 to 20 minutes following the injection of reducing agent, abrown precipitate appeared. With 1.0 g/L of PAM, there were alsoprecipitates which settled at the container bottom after 1 day of aging.With 2.0 g/L of PAM, the reaction took place quite slowly and resultedin gel formation immediately. A stable colloidal catalyst could not beobtained with PAM as the stabilizer.

Comparative Examples 6-11 Ag-PVP Catalyst System

Ag-polyvinyl pyrolidone (PVP) catalyst system was prepared as in Example2 except PASP was changed to 0.2-9.0 g/L of PVP (Fluka K25, Mw=24,000),and the concentration of each ingredient was changed as shown in Table11.

TABLE 11 Ag DMAB Temperature No. (ppm) PVP (g/L) (mmol/L) (degree C.) pH6 1080 0.2 10 22 4.6 7 1080 0.4 10 22 4.3 8 1080 1.0 10 22 4.1 9 10802.0 10 22 3.9 10 1080 5.0 10 22 3.6 11 1080 9.0 10 22 3.5

All the solutions showed turbid appearance.

The performance tests were conducted on Comparative Example 10. Theresults of coverage test are shown in Table 12.

TABLE 12 Test pH 3.5 4.5 6.0 Coverage No No No Backlight — — —

As described in the examples and comparative examples, the solution ofthe present invention (the solution comprising precious metalnanoparticle and a polymer having carboxyl group and nitrogen atom) hadhigh adsorption capability and catalytic activity as well as good bathstability compared with the solution containing other components.

What is claimed is:
 1. A solution comprising a precious metalnanoparticle and a polymer, the polymer comprises a carboxyl group and anitrogen atom within the repeating unit of the polymer.
 2. The solutionof claim 1, wherein the polymer is polyamino acids.
 3. The solution ofclaim 1, wherein the polymer is polyaspartate.
 4. The solution of claim1, wherein the precious metal is silver, gold, platinum, palladium,rhodium, ruthenium, iridium or osmium.
 5. A method for preparing asolution comprising a precious metal nanoparticle and a polymer havingcarboxyl group and nitrogen atom, the method comprises; Preparing asolution comprising precious metal ion and a polymer having carboxylgroup and nitrogen atom, Adding a reducing agent in the solution withstirring.
 6. A process for electroless plating a metal on non-conductivesurface, the process comprises the steps of; dipping a substrate to beplated into the solution of claim 1, conducting electroless plating ofthe substrate without an accelerating step.